GB978078A - Indicating instrument for graduations - Google Patents

Abstract

978, 078. Scale reading apparatus. FEINMESS DRESDEN VEB. Jan. 27,1961, No. 3297/61. Heading G2J. A scale reading instrument comprises means for optically projecting graduation lines of the scale to be read on to a micrometrically displaceable screen to bring a marking on the screen into alignment with a desired projected line, means being provided to indicate the degree of displacement of the screen, and an optical element disposed below the screen and having a central region in the form of a parallel plate with its end portions shaped to have positive lens action, a surface of the parallel plate region meeting cylindrically curved surfaces of the end portions tangentially. As shown, a scale 1 on a machine is illuminated by a lamp 14 and an image of a section thereof is projected on to a ground glass screen 6, adjustable by a rod 9 and having spaced triangular marks 17 thereon, by means of semi-reflective mirror 2, 3 and a lens. The optical correcting element 10 is situated immediately below the screen 6. In use, one of the scale 1 markings is centered between the triangular marks 17 by operation of the rod 9, and the ends of the longer markings on the scale 1 are projected on to a screen 11 by means of mirrors 15, 16, a glass plate 12 silvered at 13 preventing images of the shorter lines being projected. The screen 11 carries a scale 11a divided into 1/10ths of the distance between the longer markings on the scale 1, the scale 11a being illuminated by reflection from the silvered surface 13 and mirrors 15, 16. The amount of movement of the screen 6 is indicated on a further scale 8 mounted on the rod 9 an image of which scale is projected on to a screen 7 having a datum line, the scale 8 being graduated in 1/10ths of the scale 11a.